Broadcast Electronics 3000 Series - Page 144

CARTRIDGES IN STEREOPHONIC SYSTEMS
MAINTENANCE
Rigorous maintenance is a must for cartridges used in a stereo-
phonic system, since any distortion of the tape path can cause
phase
differences between the program material on the two tracks.
When the program material is mixed, phase differences cause de-
gradation of the frequency response.
The most important characteristic of a cartridge for stereophonic
use is the ability to consistently maintain the identical tape
path each time the
cartridge is inserted in the player. This
allows
reliable recording and subsequent accurate reproduction.
Cartridges used in a stereophonic system should initially be selected
for phase repeatability using the phasing test outlined below. This
test should be repeated on a regular basis throughout the life of
the cartridge. A cartridge which fails this test should be discarded.
To provide better guidance within the cartridge, several manufacturers
have introduced
cartridges with an adjustable corner post. The post
is threaded into the shell so that the precise post height may be
maintained. These and other cartridges designed to improve perfor-
mance should be considered for use in a stereophonic system.
STEREO PHASING TEST
Connect the output of a record/playback unit to an oscilloscope as
shown. Connect an audio signal generator to both inputs of the
recorder. While recording observe the phase of the reproduce signals.
Remove and re-insert the cartridge several times. Cartridges which
exhibit poor phase repeatability of stability should be discarded. Do
not test only for the higher frequencies, but check selected frequen-
cies across the audio band.
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